Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime
Jason W. L. Lee, Denis S. Tikhonov, Pragya Chopra, Sylvain Maclot, Amanda L. Steber, Sébastien Gruet, Felix Allum, Rebecca Boll, Xinxin Cheng, S. Düsterer, Benjamin Erk, Diksha Garg, Lanhai He, David Heathcote, Melby Johny, Mehdi M. Kazemi, Hansjochen Köckert, Jan Lahl, Alexander K. Lemmens, Donatella Loru, Robert Mason, Erland Müller, Terry Mullins, Pavel K. Olshin, Christopher Passow, Jasper Peschel, Daniel Ramm, Dimitrios Rompotis, Nora Schirmel, Sebastian Trippel, Joss Wiese, Farzaneh Ziaee, Sadia Bari, Michael Burt, Jochen Küpper, Anouk M. Rijs, Daniel Rolles, Simone Techert, P. Johnsson, M. Brouard, Claire Vallance, Bastian Manschwetus, Melanie Schnell
Abstract
Abstract Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10–100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH * , PAH +* and PAH 2+* states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH 2+ ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms.